Device pairing and authentication

1. A method implemented in a first device, the method comprising: transmitting, to a second device, a challenge message; receiving a reply message; comparing a length of time between transmitting the challenge message and receiving the reply message, to at least one other length of time between transmitting a prior challenge message and receiving a prior reply message; determining, based on the reply message, and based on the comparing the length of time to the at least one other length of time, whether the reply message was received from the second device; and communicating, based on determining that the reply message was received from the second device, with the second device.

2. The method of claim 1 , further comprising: ceasing, based on determining that the reply message was not received from the second device, communication with the second device.

3. The method of claim 1 , further comprising: sending, to the second device, a plurality of test messages; receiving, from the second device, a test result for each of the plurality of test messages; and storing, for each of the plurality of test messages, a received test result and a length of time associated with the test result, wherein the prior challenge message corresponds to a given one of the plurality of test messages and the prior reply message corresponds to a given one of the test results.

4. The method of claim 3 , wherein the transmitted challenge message comprises a selected one of the plurality of test messages; and wherein determining that the reply message was received from the second device comprises determining that the length of time between transmitting the challenge message and receiving the reply message corresponds to the length of time stored for the selected one of the plurality of test messages.

5. The method of claim 1 , further comprising: receiving a unique identifier; determining whether the first device has an associated identifier; and if the first device does not have an associated identifier, storing the received unique identifier, and changing a status identifier to indicate that the second device is paired.

6. The method of claim 1 , wherein the challenge message comprises a seed, and wherein determining that the reply message was received from the second device comprises determining that the reply message comprises a value corresponding to an expected output from a cryptographic function operating on the seed.

7. The method of claim 1 , wherein the challenge message comprises information for performing a cryptographic calculation, and wherein determining that the reply message was received from the second device comprises determining that the reply message comprises an expected value from performing the cryptographic calculation.

8. A method implemented in a first device, the method comprising: transmitting, to a second device, a challenge message including information for performing a calculation; receiving a reply message comprising a result of the calculation performed using the information by the second device; comparing a length of time between transmitting the challenge message and receiving the reply message, to at least one other length of time between transmitting a prior challenge message and receiving a prior reply message; determining, based on the result and the comparing the length of time to the at least one other length of time, that the reply message was received from the second device; and communicating, based on determining that the reply message was received from the second device, with the second device.

9. The method of claim 8 , further comprising: ceasing, based on determining that the reply message was not received from the second device, communication with the second device.

10. The method of claim 8 , further comprising: receiving, from the second device, a unique identifier; and storing the unique identifier.

11. The method of claim 10 , wherein receiving the unique identifier and storing the unique identifier comprises receiving the unique identifier and storing the unique identifier when the first device and the second device are in a secure environment.

12. The method of claim 10 , further comprising: deriving a shared secret from the unique identifier; encrypting the challenge message using the shared secret; and decrypting the reply message using the shared secret.

13. The method of claim 8 , wherein the information is for performing a cryptographic calculation, wherein the second device performs the cryptographic calculation using the information to generate the result, and wherein determining that the reply message was received from the second device comprises determining that the result is an expected value from performing the cryptographic calculation using the information.

14. The method of claim 8 , wherein the first device has stored an expected result and an expected processing time for the challenge message, and wherein determining that the reply message was received from the second device comprises determining that the result corresponds to the expected result and determining that the length of time between transmitting the challenge message and receiving the reply message corresponds to the expected processing time.

15. A device comprising: one or more processors; and a memory storing computer executable instructions that, when executed by the one or more processors, cause the device to: transmit, to an other device, a challenge message; receive a reply message; compare a length of time between transmitting the challenge message and receiving the reply message, to at least one other length of time between transmitting a prior challenge message and receiving a prior reply message; determine, based on the reply message and the comparing the length of time to the one or more other lengths of time, whether the reply message was received from the other device; and communicate, based on determining that the reply message was received from the other device, with the other device.

16. The device of claim 15 , wherein the instructions, when executed, further cause the device to: cease, based on determining that the reply message was not received from the other device, communication with the other device.

17. The device of claim 15 , wherein the instructions, when executed, further cause the device to: send, to the other device, a plurality of test messages; receive, from the other device, a test result for each of the plurality of test messages; and store, for each of the plurality of test messages, a received test result and a length of time associated with the test result, wherein the prior challenge message corresponds to a given one of the plurality of test messages and the prior reply message corresponds to a given one of the test results.

18. The device of claim 17 , wherein the transmitted challenge message comprises a selected one of the plurality of test messages; and wherein determining that the reply message was received from the other device comprises determining that the length of time between transmitting the challenge message and receiving the reply message corresponds to the length of time stored for the selected one of the plurality of test messages.

19. The device of claim 15 , wherein the challenge message comprises information for performing a cryptographic calculation, and wherein determining that the reply message was received from the other device comprises determining that the reply message comprises an expected value from performing the cryptographic calculation.

20. A device comprising: one or more processors; and memory storing computer executable instructions that, when executed by the one or more processors, cause the device to: transmit, to an other device, a challenge message including information for performing a calculation; receive a reply message comprising a result of the calculation performed using the information by the second device; compare a length of time between transmitting the challenge message and receiving the reply message, to at least one other length of time between transmitting a prior challenge message and receiving a prior reply message; determine, based on the result and the comparing the length of time to the one or more other lengths of time, that the reply message was received from the other device; and communicate, based on determining that the reply message was received from the other device, with the other device.

21. The device of claim 20 , wherein the instructions, when executed, further cause the device to: cease, based on determining that the reply message was not received from the other device, communication with the other device.

22. The device of claim 20 , wherein the instructions, when executed, further cause the device to: receive, from the other device, a unique identifier; and store the unique identifier.

23. The device of claim 22 , wherein receiving the unique identifier and storing the unique identifier comprises receiving the unique identifier and storing the unique identifier when the device and the other device are in a secure environment.

24. The device of claim 22 , wherein the instructions, when executed, further cause the device to: derive a shared secret from the unique identifier; encrypt the challenge message using the shared secret; and decrypt the reply message using the shared secret.